1. Field of the Invention
The present invention is directed to a process and apparatus for the gas phase polymerization of olefins. More particularly, the present invention is directed to a process and apparatus for polymerizing at least one olefin monomer in the presence of a catalyst system whose components are separately introduced into a gas phase reactor in close proximity to each other.
2. Background of the Prior Art
Gas phase processes and apparatus for the polymerization of at least one olefin are well known in the art. Among recent processes and apparatus developed for this purpose are systems wherein the catalyst components that constitute the catalyst system utilized in the olefin polymerization are separately introduced into the polymerization reactor.
More specifically, it is known in the art to separately introduce, into a tubular gas phase reactor, a solid catalyst component and a cocatalyst component. That is, a solid catalyst component, which includes at least one transition metal, is introduced into the polymerization reactor separately from the cocatalyst component, which typically is an organometallic compound of a metal of Group 1, 2 or 13 of the Periodic Table. The organometallic compound of the cocatalyst component is preferably a hydrocarbyl-containing compound which includes a metal of Group 1, 12 or 13. More preferably, the cocatalyst component is an alkyl-containing compound which includes at least one of the aforementioned metals. The organometallic compound, which acts as the cocatalyst component, may optionally include halogen or hydrogen atoms and thus be a halide or hydride compound.
These processes and apparatus are specifically designed to provide processing improvements over earlier olefin gas phase polymerization processes and apparatus. None of these recently developed systems, however, have adequately addressed certain well known problems associated with such processes and apparatus. Specifically, although the aforementioned recent developments are designed to eliminate operability problems, such as problems associated with catalyst clumping, which adversely affects operability, i.e. large catalyst particles tend to plug polymerization reactor withdrawal system, such as outlet conduits and the like, these developments have not fully addressed the associated problems of producing polymers having the necessary physical properties to meet specific customer needs.
The most pertinent examples of the prior art, which illustrates gas phase polymerization of olefins wherein the catalyst and the cocatalyst components are separately introduced into the polymerization reactor, include U.S. Pat. No. 2,846,426 to Larson et al. In this process an ethylene gas stream is introduced into liquid titanium tetrachloride. The thereupon vaporized titanium tetrachloride is, in turn, introduced into a polymerization reactor. At the same time, a second ethylene gas stream is introduced into liquid diisobutylaluminum hydride to form a second vaporous composition which is also fed, through a separate inlet, into the same polymerization reactor. A third ethylene gas stream is separately introduced into the reactor. This scheme permits not only gas phase polymerization of ethylene but, in addition, in-situ formation of the catalyst system which catalyzes this polymerization reaction. This processing scheme is alleged, in the '426 patent, to improve control of active catalyst concentration relative to the concentration of the polymerizable ethylene.
U.S. Pat. No. 2,939,846 to Gordon et al. describes a process wherein two separate inert gas streams entrain the vapors of two catalyst components of a Ziegler catalyst system utilized in olefin polymerization reactions. One of the inert gas streams entrains a vapor of a reducing compound, i.e. an aluminum-containing compound. The other inert gas stream entrains a vapor of a salt of a metal of Groups IV to VI of the Periodic Table. A particularly preferred metal of Groups IV to VI, preferred in the '846 patent, is titanium. Also, in a preferred embodiment of the invention of the '846 patent the olefin monomer is used as the entraining gas. The two separate gas streams are intermixed at a temperature at which the reducing compound and the salt of a metal of Groups IV to VI are vaporizable. The olefin monomer is thereupon passed through a point at which the two gaseous streams intermix to form the solid catalyst. In an alternate embodiment, the solid catalyst product is deposited in a polymerization reactor.
U.S. Pat. No. 4,035,560 to Caumartin et al. is directed to a fluidized bed olefin polymerization process wherein a first catalyst component, comprising the solid product of reaction of a transition metal compound and an organomagnesium compound, which may or may not be supported on an inert carrier, is entrained by the upward flow of a gaseous mixture which contains hydrogen and one or more olefin monomers. The thus formed fluidized bed also includes a second catalyst component, an organometallic compound of a metal of Group II or III of the Periodic Table, disposed on an inert porous support separately introduced into the reactor.
U.S. Pat. No. 4,302,566 to Karol et al. sets forth a continuous process for ethylene copolymer production employing a gas phase fluidized bed vertical tubular reactor. A catalyst system is provided by a so-called precursor composition which is the solid reaction product of magnesium chloride and titanium tetrachloride. This "precursor composition" is activated in one of two ways. In the first, the precursor composition is slurried in a solution of the activator compound, triethylaluminum. The thus coated solid particles are thereupon dried and introduced into a vertical disposed tubular reactor downstream of the point of introduction of the monomer or monomers. In addition, supported activator particles, formed by slurrying an inert support in a solution of triethylaluminum followed by the driving off of the solvent, is introduced into the reactor along with the activated precursor composition.
In an alternative embodiment, the triethylaluminum may be introduced in the liquid state by merely introducing a liquid solution of triethylaluminum in an inert hydrocarbon at the same position in the reactor as is the activated precursor solid composition. This second activation embodiment is very similar to the first described activation process except that the solid precursor composition particles and the solid aluminum disposed on an inert support are premixed prior to their introduction together into the reactor.
U.S. Pat. No. 4,665,143 to Ahluwalia et al. sets forth a process for polymerizing olefins in a vertical tubular reactor. An olefin monomer or monomers is introduced into a reactor in a gaseous stream at the upstream, bottom end of the reactor. A first catalyst component, the reaction product of a transition metal compound and a metal alkyl of a metal of Group IA, IIA or IIIB, disposed on an inert support, is introduced downstream of the point of introduction of the monomeric gas stream. A second catalyst component cocatalyst, an aluminum alkyl, is introduced with the olefin monomer into the reactor in an inert hydrocarbon liquid solution above and downstream of the introduction point of the first catalyst component. The distance between the introduction of the first and the second catalyst components is at least two mixing distances. A mixing distance is defined as the distance, measured from the injection point, where only an equilibrium concentration of the introduced substance is present. This mixing distance limitation is said in the '143 patent to insure against the formation of "hot spots," and to minimize "lump" formation.
U.S. Pat. No. 4,921,919 to Lin et al. is directed to a process and apparatus for the polymerization of an olefin monomer, preferably propylene, in a vapor phase tubular horizontal reactor. A titanium-containing first catalyst component is introduced into the top side of the horizontal reactor adjacent to its upstream end. A second and a third catalyst component, i.e. a cocatalyst and a modifier, respectively, are also fed into the top side of the horizontal reactor vessel, downstream of the point of introduction of the first catalyst component. This downstream distance is at least 25% of the internal diameter of the tubular reactor. This minimum distance is needed to minimize formation of polymer lumps.
The above described processes and apparatus of the most pertinent prior art references provide improvements in gas phase olefin polymerization operability. However, these processes and apparatus do not address the need in the art for olefin polymeric products having the desired crystallinity and strength properties required of high strength olefin polymers. Thus, there is still a need in the art for an improved gas phase olefin polymerization process and apparatus which provides not only improved operability but an olefin polymer product having improved physical properties.